Photographic developer



Patented June 27, 1939 NITED STATES PATENT OFFICE rnorocnsrmc nEvELorEn Edmund W. Lowe, Chicago, ilL, assignor to The Edwal Laboratories, Inc., Chicago, 111., a corporation, of Illinois No Drawing. Application September 20, 1937,

Serial No. 164,703

12 Claims. (on. 95-88) to the increased use of cameras employing negatives of such a small size that the print is made by projecting the film image onto the photolj graphic paper insteadof printing by direct contact. Conversely, improvements in films and improvements in fine grain developers have made possible the increased use of miniature cameras,

so that the'production of improved fine-grain 20 developers cannot be said to be merely in response to the demand for the production of imagesbf the fine-grained or even-grained type.

80 called coarse-grained images, I have deter- I mined, result very largely, if not entirely, from 2 a clumping up of silver particles during development, with the result that the particles, instead of being evenly distributed throughout the emulsion, are found in patches or clumps distinctly discernibleunder a microscope. The result is I that, if a negative developed in the ordinary way so as to produce a coarse grain is enlarged only very slightly, the print. has a mottled and uneven appearance. Even some of the so-called finegrain developers will show a certain amount of 85 graininess if a degreeof enlargement be attempted appreciably in excess of 4 or 5 diameters, although some fairly satisfactory fine-grain negatives have been produced by some oath finegrained' developers which can be enlargedat I do proximat'ely'20 diameters without-appreciabl development of a mottled or grainy appearance.

Borne fl ne grain developers have also been suggested which produce negatives capable of enlargement in excess of to diameters, indeed 46 up to 50 or 60 diameters, without appreciable graininess in the enlargement. All of these developers with which I am familiar, howeve have certain disadvantages. The marked disadvan-w tage of one type of fine-grain developer is that 60 the negatives produced tend to be rather flat and the films must be exposed to light while in the camera fifty to one hundred percent longer in order to obtain sufiicient density in the negative. Other fine-grain developers capable ofvery great 66 enlargement without the development of graininess have the disadvantage that the negatives developed in them tend to have blocked-up highlights unless the developing time be very carefully regulated. Another disadvantage found in substantially all fine-grain developers produced heretofore is that they tend to produce a coarser grain than otherwise if the negative has been over-.

exposed. They also have the disadvantage that, while the negatives are capable of very great enlargement without the appearance of grain, the enlarged images tend to lack critical definition, I and-the very large pictures produced do not faithfully record the surface texture of objects photographed.

It is the object of my present invention to develop fine-grained images in a more satisfactory manner than has been done heretofore.

A further object is to provide an improved finegrain developer which produces very fine, evengrained images without the disadvantages inherent in negatives produced by previously known fine-grain developers.

In general, I. accomplish the objects of my invention by the use of primary and secondary developing agents of a character to be defined hereinbelow, a substance capable of forming soluble, substantially stable complexes with the silver of a relatively strong base, the developing solution as a-whole having a pH of 7 to 7.8 and particularly in certain preferred embodiments from 7.3 to 7.5. The foregoing general identification of the developer of my invention is, of course, to be understood in the light of the more particular consideration of the ingredients as discussed hereinbelow. In general, it may be stated, however,

that I may, under certain circumstances, dispense with the use of the secondary developing agent, in which case somewhat modified results are obtained.

The primary developing agent which I employ is p-methylaminophenol or one of its salts, such as the sulphate commonly known as metol. (The terms elon, rhodol and pictolare employed in the trade to identify the same compound.)'

I may also employ p-methylaminocresol, with the methyl group of the cresol in either of the two possible positions, but, in general, I

duction potential.

ing agent being one having a relatively low re- The second developing agent salts of the emulsion, and a soluble sulphite salt as to produce the desired pH in the solution of the final composition. I may employ any soluble sulphite of an alkali or alkali earth metal or a soluble sulphite of an organic base. Preferably, I use sodium sulphite in amounts to introduce 50 to 150 grams of sodium sulphite per liter of water. Ammonium chloride is the preferred substance of the group defined as substances capable of forming substantially stable complexes with silver salts, but ammonium salts of relativelystrong acids having a pH in solution of less than 6 will function satisfactorily as well as certain amine salts and sodium thiosulphate. The latter compound, however, must be used with very great care and in very small proportions, and those proportions must be properly balanced with respect to' the other chemical or desirable results will not be obtained.

Before referring to specific examples, I wish to point out that the primary developing agent which I employ is one which is sufllciently energetic to produce a satisfactory image in a reasonable length of time when the pH of the developing solution lies between 7 and 7.8. Moreover, the primary developing agent which I employ is and must be "soft-working", that is, used alone, it must not produce negatives of high contrast unless the developing time is unduly prolonged. The primary developing agents identified hereinabove have these properties. Obviously, therefore, if a relatively soft negative image is desired, the secondary developing agent need not be employed. The secondary developing agent, however, as described a developing agent of relatively low production potential, results in the development. of an image with strong contrast without aifecting the fine grain of the image deleteriously.

The following examples illustrate compositions for producing fine-grained images on photographic negatives, all of these examples coming within the scope of the general description of my invention contained hereinabove.

Ammonium chloride do are-moo Example 4 Distilled water liter 1 p-Methylaminophenol sulphate grams 8 p-Hydroxyphenylglycine do 8 Sodium sulphite do 100 Sodium thiosulphate do 0.5

Example 5 Water liter 1 I p-Methylaminophenol hydrochloride grams 8 Chlorohydroquinone do 5 Sodium sulphite do 120 Ammonium chloride do Example 6 Water liter 1 p-Methylaminophenol sulphate grams 2 p-Hydroxyphenylglycinedo 1 Sodium sulphite do 90 Ammonium chloride do 10 The pH of the solutions given in the examples hereinabove is, in each case, between 7 and 7.8, and, for the most part, fairly close to 7.4. While the examples are given as indicating water solutions, it is to be understood that the common way of marketing my developer is to sell it as a dry mixture, and so proportion the ingredients that, when a given quantity of the mixture as a whole is dissolved in a given quantity of water, a suitable developing solution will be produced. It is to'be noted that Examples 1 to 5, inclusive, show solutions which are suitable for developing several rolls of film. Example 6, however, illustrates a formula good for developing only a single roll of film, and the solution can then be discarded as worthless. I may also prepare stock solutions of my developer which can be diluted down to the desired strength, although, when employing my preferred group of ingredients and producing a solution capable of developing several rolls of film, the total amount of material in solution is such that a stock solution cannot be produced which is capable of dilution to such an extent as to warrant its use under ordinary circumstances.

It will be noted that Examples 1 to 3, inclusive, show decreasing proportions of the secondary developing agent, in this case p-hydroxyphenylglycine. Example 1 can be employed to produce relatively sharp images, and the amount of contrast obtainable decreases from Example 1 through Example 3, the latter producing images with considerably less contrast than Example 1. By leaving out the secondary developing agent entirely, the amount of contrast can be still further decreased.

Each of the examples given above employs a substance capable of forming a fairly stable water soluble complex with silver bromide, in all cases except one ammonium chloride being the ingredient inquestion, the other case being Example 4 where sodium thiosulphate is substituted. As stated previously, the proportion of sodium thiosulphate employed is apt to be very critical and, in the example given, if more than half a gram of sodium thiosulphate be employed, there will be a strong probability if not a certainty of getting a foggy image as a result. For this reason, I prefer to employ ammonium chloride or other ammonium salt. It is not absolutely necessary, however, that ammonium chloride or a similar agent be used, although much more dependable results are obtained by its use. Should those skilled in the art wish, for any reason, to avoid the use of ammonium chloride, they may in part make up for its loss by increasing somewhat the amount of sodium sulphite used. The sodium sulphite in the fine-grain developer of my present invention has a three-fold function. In the first place, it has a. buffer action. Secondly, it exerts a solvent action on silver bromide and this accounts for the fact that to some extent the chloride may be compensated for by increasing the proportion of sulphite. 'I'hirdlv, the sodium sulphite has a preserving action, it being well known that it has been employed primarily as a preservative in many commercial developers used in the past. With-respect to the solvent action of sodium sulphite, it is to be noted that, in general, it tends to form soluble complexes with si1-' ver bromide, but these soluble complexes are not sufiiciently stable to prevent precipitation of silver bromide out of solution under certain conditions. Indeed, the complex molecules formed with ammonium chloride and silver bromide are not entirely stable but they are appreciably more stable than the soluble complexes including so.- dium sulphite and are adequately stable to produce the results desired. Accordingly, when I refer to the production of substantially stable complexes with silver bromide, this expression may be interpreted as meaning more stable than the complexes formed by the use of sodium sulphite. 80 In general, I may secure the objects of my invention if I employ ingredients selected from the groups or classes discussed hereinabove, and control the proportion of ingredients so that the pH of the developing solution is somewhere between I and 7.8. Ifind, however, that in general the advantages of my invention are more marked if the pH of the developing solution is between 7.3

and. 7.5, particularly when the preferred ingredients are employed, namely, thespecific ingredients given in Example 1. As noted with respect to this particular example, the pH is 7.4. This particular formula may be modified slightly, however, to bring the pH down slightly below 7 .4, say'7.34, and for some purposes somewhat improved results even can be obtained than with the specific formula of Example 1. It is to be noted that all-of the ingredients given in Example 1, with the exception of the sodium sulphite, possess an acid reaction in solution. Sodium. sulphite is a mild alkali, a 10% solution of sodium sulphite having a. pH of only 9.7. Indeed, .,,iii,.;ordinary photographic work, sodium sulphite is never considered ,an alkali, so that in the parlance of the industry,'the developer of my invention does not -use an alkali. Nevertheless, by thebufier action of the sodium -sulphite, the pH of the solution as a whole may be controlled, and the proportion of sodium sulphite may be modified for this purpose. With respect to modifying the proportions 60 01' ingredients given in Example l, it'rnay be stated that the "metoP may be present in the final solution (the solution being based on the use of one liter of water) in proportions of 1 to 20 grams, the glycine in proportions of from 66 1 to 15 grams, the sodium sulphite in proportions of from 50 to 150 grams, and the ammonium chloride in proportions up'to approximately grams. .Whatever the proportions may be, the ingredients may be balanced so that the pH of 70 the final solution is withinthe broad. range defined, but-preferably within the specific range discussed he'reinabove, namely from 7.3 to 7.5.

' The developing characteristics of my improved fine-grain developer are such that in general 76 somewhat longer time may be required than isnormally required when employing so-called finegrain developers marketed before my invention. For the further understanding of those skilled in the art, I give below the approximate developing time for different types of films based upon the use of a developer substantially identical in proportions of ingredients and strength of solujtion given in Example 1.

(1) For fine-grain panchromatic films such as du Ponts lviicropan or Agfa Finopan '7 to 10 (2) For most ordinary emulsions of both 1 the panchromatic and orthochromatic type 16 to 20 .(3) For slow developing films such as Selo hypersensitive panchromatic 25to 30 The outline of developing time given above is not meant to be exhaustive but only sufiiciently representative so that those skilled'in the art will in general be able to gauge developing time ior'any particular kind of film from this general outline. It is a characteristic of this developer that when several rolls of film are developed in j the same solution, the development time must be increased somewhat for each successive roll in order to obtain the same contrast. I

The improved developers of my invention produce negatives having exceedingly fine,. even grain, so that enlargements up to 50 diameters and more can be made from them without difficulty. Furthermore, the big enlargements from such negatives reproduce the outline of the original accurately, and the surface texture of the subject photographed is reproduced with much greater fidelity than enlargements from negatives processed from older types of so-called finegrain developers. It is a marked characteristic of my new developing solutions that the negatives developed by their use do not readily lose detail or block up in the regions of highlight, as is usually found to be the case in older types of fine-graindevelopers. vention, whether in the dry form or in solution,

keeps well, does not stain the hands or clothing in the normal course of photographic processing, and generally, from a practical standpoint, is very satisfactory in those properties whichare not so directly concerned with the finished negative.

I negative when there is an appreciable variation in the developing time. However, when the developer of my invention is employed, there may be quite aconsiderable variation in the developing time and this does not cause extreme variathus in the quality of the negative providing reasonable care otherwise is used. The second important characteristic is that negatives which have been subjected to considerable over-expo- Minutes The developer of my in- Additional advantages and important characsure, and hence possess a high density, do not negative. Indeed, negatives may be exposed up to ten times the normal amount forgiven conditions, and the negative so exposed can be developed by means of my developer without the production of coarse grain. Needless to say, over-exposure of such duration is not recommended, but the fact that such an over-exposed negative may be developed and a fine-grain image produced by my developer, illustrates the point .enlargements may be made'from films which have all of the appearance of contact prints made from relatively very much larger films, and the surface texture of such substances as sand, snow, skin, cloth, trees, grass and the like is reproduced so faithfully that results can be obtained in no sense .obtainabie with other developers with which I am familiar.

I have described my invention in relatively great detail for the benefit of those skilled in the art but it is understood that the scope of 'my invention is limited only by the definitions thereof contained in the appended claims.

What I claim as new and desire to protect by Letters Patent of the United States is:

l. A fine grain photographic developer comprising a developing agent of a class consisting of paramethylaminophenol, paramethylaminocresols, and their salts, an ammonium salt of a relatively strong acid, and a soluble sulphite, the proportions of ingredients being balanced so that the developer in solution has a pH of 7 to 7.8.

2. A fine grain photographic developer comprising a developing agent of a class consisting of paramethylaminophenol, paramethylamino cresols, and their salts, an ammonium salt of a relatively strong acid, and a sodium sulphite, the

proportions of ingredients being balanced so that the developer in solution has a pH of 7 to 7.8.

3. A fine grain photographic developer comprising as' a main developing agent paramethylaminophenol or one of its salts, a secondary developing agent of relatively low reduction potential capable oi functioning in substantially neutral solutions, an ammonium salt of a relatively strong acid, and a soluble sulphite, the proportions of ingredients being such that the developer in solution has a pH of 7 to 7.8.

4. A fine grain photographic developer comprising as a main developing agent paramethylaminophenol or one of its salts, .a secondary developing agent of relatively low reduction potential capable ofiunctioning in substantially neutral solutions, ammonium chloride, and a soluble sulphite, the proportions of ingredients being such that the developer in solution has a pH of 7 to 7.8.

5. A fine grain photographic developer comprising as a main developing agent paramethylamino- -phenol or one of its salts, parahydroxyphenylglycine, ammonium chloride, and a soluble sulphite, the proportions of ingredients being such that the developer in solution has a pH L7 to 7.8.

6. A fine grain photographic developer comprising as a main developing agent paramethylaminophenol or one of its salts, a secondary developing agent of relatively low reduction potential capable of functioning in substantially -'neutral solutions, ammonium chloride, and

sodium sulphite, the proportions of ingredients being such that the developer in solution has a pH of 7 to 7.8.

7. A fine grain photographic developer-comprising p-methylaminophenolsulphate, 1 to 20 parts; p-hydroxyphenylglycine, 1 to parts; sodium sulphite, 50 to 150 parts; and ammonium chloride, 1 to 30 parts, said developer having a pH of 7 to 7.8, and possessing the property of producing extremely fine grain images with sharp outlines and ample detail in the highlights.

8. A fine grain photographic developer comprising as a primary developing agent p-methylaminophenol or one of its salts, a secondary developing agent of relatively low reduction potential, a soluble ammonium salt having a pH in solution lower than 7, and a suilicient amount of a soluble sulfite having a pH in solution greater than 7 toproduce a developing composition which.

what lesser proportion of ammonium chloride,

and enough sodium sulphite to cause the developer as a whole, in solution, to have a pH 0! between 7.0 and 7.8.

11. A fine grain developer comprising metol" as a primary developing agent, up to substantially equal proportions of asecondary developing agent of low potentiahammonium chloride, and enough sodium sulphite to cause the developer as a whole, in solutiomto have a pH of about 7.4:.

' 12. A fine grain'developer comprising the fol-:

lowing ingredients in the proportions called for: meto about 8 grams; glycine, about 8 grams; ammonium chloride, about 5 grams; and sodium sulphite, about grams; said developeradapted to be dissolved in water to produce a solution having a pH of approximately 7.4.

EDMUND W. LOWE." 

